Went to visit, stayed for the giant spiders. —

How many people did it take to colonize Australia?

A new study suggests a large, deliberate migration from Wallacea.

Enlarge/ Norman Tindale, pictured here in 1927 with members of a local Aboriginal group, led a mission to gather precise ethnographic and geographic data from many different Aboriginal groups. He also gathered hair from the people he interviewed, which provided DNA samples for earlier studies. The group here is at Rockshelter at Bathurst Head (Thartali) in eastern Cape York Peninsula.

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A new study suggests that the first humans to move into Australia and New Guinea came in larger numbers—and perhaps with more of a plan—than some researchers previously thought.

People have lived in Australia and New Guinea since at least 60,000 years ago, when sea levels were about 100 meters (300 feet) lower than today. Due to lower sea levels, a land bridge across the Torres Strait linked Australia and New Guinea into a single landmass (termed Sahul). The first humans to set foot on Sahul probably arrived via closely spaced islands that stretched like stepping-stones across the 1,800km (1,100 miles) of ocean from the exposed continental shelf of Southeast Asia. And a new study suggests that it would have taken at least 1,300 people crossing these islands to give us a lasting foothold.

Playing on hard mode

Trying to colonize a new, uninhabited land is a challenge. If you bring too many people at once, the sudden influx could put too much strain on local resources, and everyone would die. But if you don’t bring enough people to reproduce and maintain genetic diversity, each generation gets smaller until the group eventually runs out of people and everyone dies. Flinders University ecologist Corey Bradshaw and his colleagues wanted to figure out how many people needed to settle in Sahul to make sure humans didn’t end up going locally extinct.

Archaeologists usually assume that people who made their living hunting, gathering, and fishing in the past probably lived similar lifestyles to modern hunter-gatherers. That means their life expectancy, fertility rate, and the length of their generations should be pretty similar. Bradshaw and his colleagues used what we know about modern hunter-gatherers to build a computer model of the first people to move into Sahul.

They tested several scenarios to figure out how many people needed to arrive in the first few centuries in order to minimize the odds of the population dying out. The answer turned out to be somewhere between 1,300 and 1,550 people, assuming about half of them were women. That left just a 10% chance of extinction after 100 generations—still a risky venture, but not an implausible one.

An organized effort

The first people who reached Australia probably did so accidentally, perhaps blown across the ocean by a chance storm from one of the islands of the region called Wallacea—maybe Sulawesi, Timor, Flores, or one of dozens of smaller islands that mostly belong to modern Indonesia. But at some point, someone must have returned to tell the tale, and people must have started making the trip on purpose. The model suggests “probably deliberate migration, given the numbers of people involved,” Bradshaw and his colleagues wrote.

That doesn’t necessarily mean that more than a thousand people piled into a single massive fleet of boats and set sail to colonize a new land all at once. According to the model, if a new group of about 130 people arrived every 70 to 90 years, that would be enough to maintain the colony’s chances of survival. Of course, the chances of extinction increased with longer gaps between new arrivals.

Even so, sending off groups of 130 settlers at a time suggests that the islands of Wallacea were home to more people, or at least denser groups of people, during the Pleistocene than archaeologists have previously assumed. The effort would have taken a group of around the size that modern hunter-gatherers in Australia and New Guinea usually only pull together for large ceremonial gatherings, which implies some impressive organizing. We currently have no way of knowing whether some kind of central leadership or agreement drove the effort or whether several small groups banded together to share an adventure.

More evidence needed

Of course, it’s always technically possible that a much smaller group of settlers arrived, facing much greater odds of eventual extinction, and somehow came out on top. It’s just much less likely. But any model requires hard evidence to test it, which means we need more archaeological finds and ancient DNA samples.

Ancient DNA evidence in this case is sparse, thanks to the region’s combination of heat and moisture. But previous studies on samples of indigenous Australian DNA suggest that a founding group of just 36 to 50 women could have produced all the mitochondrial DNA groups found in today’s indigenous Australians (as a quick review, mitochondrial DNA is passed directly from mother to child, so it’s a great way to trace a specific maternal lineage).

That’s a much smaller group of people than Bradshaw and his colleagues’ model calls for. But it also assumes that the maternal lineages of modern indigenous Australians were the only ones present when the first humans arrived. And given the continent’s history, that’s not necessarily a likely assumption.

So far, the oldest known evidence of human presence in Australia is at Madjedbebe Rock Shelter, which dates to 60,000 to 70,000 years ago. Archaeologists have found several other sites at least 47,000 years old, but much of the archaeological record from the days of the first humans to arrive—if it’s still preserved anywhere—remains undiscovered.

91 Reader Comments

I would think if anything, the odds of them having the "right number" of people for a good statistical chance of success, would be low. Not like they would have had the chance to run experiments and know what that number was.

For that matter, I suspect that coming in with too many people, then having half of them die, would look about the same from our modern genetic perspective as them arriving with half as many people to start with.

I would think if anything, the odds of them having the "right number" of people for a good statistical chance of success, would be low. Not like they would have had the chance to run experiments and know what that number was.

For that matter, I suspect that coming in with too many people, then having half of them die, would look about the same from our modern genetic perspective as them arriving with half as many people to start with.

They did not die out does not mean they had good odds to start with. Also the model assumes they were hunter-gatherers when there is growing evidence to contradict this as the only part of their lifestyles - it is more regional dependent.

An optimal solution is really only optimal if you get to play more than once - say playing CIV. For a real life chance for this we may see multiple colonization attempts of our Moon and Mars to try and establish a permanent human presence.

As for the Australian Aboriginals they managed to survive in a large variety of areas in Australia and thrive in some too. Having worked in the Outback it is an impressive feat to think what they achieved.

It required technology (boats or rafts) to get to an island, but the reward was a new land with wildlife that had never seen humans before (and had no fear), plus unexploited plants and shellfish beds. Australia was the biggest island of all. It was a bonanza, at least for the first few centuries before the large land marsupials were hunted to extinction. The ancestral Aborigines were involved in one of the earliest and largest high-tech booms in human history.

I'd almost say that 130 people every 70 to 90 years might even be on the low side, with the continent seeming like everything, up to and including the grass and many of the rocks, seem to be poisonous, dangerous and/or lethal to humans in some way.

There are some serious ocean crossings involved in this migration. While not extreme distance they are extremely treacherous due to depth and currents. This is not something you could expect to cross with a raft. Boatbuilding nearly certainly would have been a required skill.

If you have ever been out on the open ocean 90km is a very long way. Even in a power boat. In a raft it would be nearly impossible. I stand by my statement that boatbuilding would nearly certainly be a requirement.

Have Australia's aboriginal people retained any boat making skills? I know it's a long time, but it seems weird to me that a people skilled addy seafaring would give up the seafaring (not saying it's unlikely or implausible, it just intuitively feels like the kind of thing you wouldn't abandon).

If you have ever been out on the open ocean 90km is a very long way. Even in a power boat. In a raft it would be nearly impossible. I stand by my statement that boatbuilding would nearly certainly be a requirement.

Have Australia's aboriginal people retained any boat making skills? I know it's a long time, but it seems weird to me that a people skilled addy seafaring would give up the seafaring (not saying it's unlikely or implausible, it just intuitively feels like the kind of thing you wouldn't abandon).

The Tasmanians lost boat-building and IIRC were still paleolithic when they were discovered and wiped out by Europeans. Their population was too small to have retained that knowledge and they were too far offshore for mainland Aborigines to be in contact.

I would think if anything, the odds of them having the "right number" of people for a good statistical chance of success, would be low. Not like they would have had the chance to run experiments and know what that number was.

For that matter, I suspect that coming in with too many people, then having half of them die, would look about the same from our modern genetic perspective as them arriving with half as many people to start with.

This is an interesting hypothetical question, raised in the article, but we start from the certain knowledge that the colonization was successful. I imagine that implications relate to how we research the likely migration paths, and think about what sorts of evidence (in what amounts) we need to look for.

The first people to arrive would have encountered mega fauna which were not familiar with pack hunting humans. These large marsupials, flightless birds and reptiles would have been relatively easy prey. In particular, Meiolania, a giant land turtle, would have made for quite a feast. With no other human or placental mammal competition (dogs, aka dingos didn't arrive until later), the first humans should have had an easy life and rapidly increased in numbers.

Let me emphasize, when the first humans reached Australia, there were zero placental mammal predators. The dingo (dog) was not present. It was brought to Australia some 10,000 years later. The top large predators were giant monitor lizards (including the Komodo Dragon) one of which was 23 feet long, 16 foot long land crocodiles, 500 pound flightless carnivorous birds, and a 300 pound marsupial "tiger". The plant eating animals included, but not limited to a giant 500 pound kangaroo, a three ton wombat, a 500 pound land turtle which had a club tail, a sheep size monotreme, and a 1,000 pound "thunder" bird.

Although these sound scary, they were dumb and slow. They would have all been relatively easy prey for the first humans. In contrast the animals in North America were modern placentals with speed and brains. (Lions, saber toothed cats, bears, wolves)

I think just a small group of castaway humans would have done well. Others probably followed, but for the first humans it would have been a hunter gatherer dream time.

Have Australia's aboriginal people retained any boat making skills? I know it's a long time, but it seems weird to me that a people skilled addy seafaring would give up the seafaring (not saying it's unlikely or implausible, it just intuitively feels like the kind of thing you wouldn't abandon).

The migration across the Pacific covered journeys of thousands of kilometres, so 90km is a stone's throw by comparison. Granted the timeframes and level of technological sophistication may be different.

If you have ever been out on the open ocean 90km is a very long way. Even in a power boat. In a raft it would be nearly impossible. I stand by my statement that boatbuilding would nearly certainly be a requirement.

Have you heard of Thor Heyerdahl and the Kon-Tiki expedition? They did 4300 miles (6900 km) on a balsa wood raft - just to prove that South Americans could have populated the Polynesian islands.

I'd almost say that 130 people every 70 to 90 years might even be on the low side, with the continent seeming like everything, up to and including the grass and many of the rocks, seem to be poisonous, dangerous and/or lethal to humans in some way.

Naw, when the Aboriginals arrived, most of the animals were large, tasty, and not sufficiently wary. Those ones got eaten; and now the continent only has left those which are toxic, angry, poisonous, fast moving or all four..

Australia: everything here wants to kill you; because the ones that weren't as aggressive got eaten.

(I have heard a similar process has happened in the Cook Islands - all the reef fish around the main islands are poisonous and the fish for eating are caught on outer islands or in the open ocean; because the islands have been inhabited long enough for the tasty local fish to have all been eaten)

I'm assuming that the sharks back then would have been as hungry and aggressive as the ones encountered and recounted by sailors and pilots during the Pacific war. For a migration, I'll imagine some sturdy boats were used.

I would think if anything, the odds of them having the "right number" of people for a good statistical chance of success, would be low. Not like they would have had the chance to run experiments and know what that number was.

For that matter, I suspect that coming in with too many people, then having half of them die, would look about the same from our modern genetic perspective as them arriving with half as many people to start with.

And in reality, the first people probably arrived by accident, and the next people probably arrived by accident, and at some point, someone made it back the other direction and set up a trade network.

After that, you'd have professional traders making the journey, bringing along a few other people each time, possibly in both directions. There'd probably be a few times when the few traders all got wiped out, resulting in extended periods of no travel, followed by someone who figures it out again and meets up with these other people groups.

I know these are hunter/gatherer groups, but people have been trading things for a long time too.

As a result, the first people to settle New Guinea probably didn't survive -- but knowledge of the things to hunt and gather there did. So larger parties would be sent out, and some of them wouldn't come back. There'd be trade of both goods and of people in both directions.

Once a stable population was established in New Guinea, it would have started foraging and expanding in the direction of Australia, eventually circumnavigating the continent, with the aid of supplies from the New Guinea settlement areas.

I'd almost say that 130 people every 70 to 90 years might even be on the low side, with the continent seeming like everything, up to and including the grass and many of the rocks, seem to be poisonous, dangerous and/or lethal to humans in some way.

Naw, when the Aboriginals arrived, most of the animals were large, tasty, and not sufficiently wary. Those ones got eaten; and now the continent only has left those which are toxic, angry, poisonous, fast moving or all four..

Australia: everything here wants to kill you; because the ones that weren't as aggressive got eaten.

(I have heard a similar process has happened in the Cook Islands - all the reef fish around the main islands are poisonous and the fish for eating are caught on outer islands or in the open ocean; because the islands have been inhabited long enough for the tasty local fish to have all been eaten)

If you have ever been out on the open ocean 90km is a very long way. Even in a power boat. In a raft it would be nearly impossible. I stand by my statement that boatbuilding would nearly certainly be a requirement.

The Kon-Tiki expedition crossed 4,300 miles of the Pacific on a raft. The same man also crossed 4000 miles of the Atlantic on a raft.

There are some serious ocean crossings involved in this migration. While not extreme distance they are extremely treacherous due to depth and currents. This is not something you could expect to cross with a raft. Boatbuilding nearly certainly would have been a required skill.

Why assume people were stupid then? If your people lived on a rather small island then THE tech of the day is "Boating".

If you have ever been out on the open ocean 90km is a very long way. Even in a power boat. In a raft it would be nearly impossible. I stand by my statement that boatbuilding would nearly certainly be a requirement.

Have Australia's aboriginal people retained any boat making skills? I know it's a long time, but it seems weird to me that a people skilled addy seafaring would give up the seafaring (not saying it's unlikely or implausible, it just intuitively feels like the kind of thing you wouldn't abandon).

There is evidence of lightweight canoes made of bark over a wooden frame in use before the 17th century and dugout canoes replacing them after the 17th century. There is no evidence of continuous seafaring but the number of finds from the deep past is low that really doesn't mean anything.

I'd almost say that 130 people every 70 to 90 years might even be on the low side, with the continent seeming like everything, up to and including the grass and many of the rocks, seem to be poisonous, dangerous and/or lethal to humans in some way.

It's really not that bad.

There are some very poisonous snakes but we're too big to eat so they stay away from us.

Crocodiles are a genuine threat but only in water. On land humans can sprint a faster than the crocodiles found in Australia, and we can maintain our speed over much longer distances. Give the human a weapon, such as a sharpened stick, and the crocodile will have to run for its life.

Some plants are poisonous if you eat them. But our taste buds detect the danger and they're disgusting. Some of them can be processed, which both removes the toxins and the bad taste.

That's about it really for threats to humans.

The apex predator on land is the dingo. They're intelligent enough to recognise how dangerous humans are and avoid us. If you corner a dingo and force it into a fight they're likely to surrender - in the canine equivalent of raising a white flag. Lay down, head on the ground, stay still, hope you go away.

Living among dingos on the mainland, you only ever come across them while travelling at high speed in a car and only briefly before they run off. You might wake up every morning and find your house surrounded by their footprints, but you'll almost never see them. I've only seen them regularly on a small island off shore which was packed with tourists and they'd learned we just want to take a photo. Those mostly dingos ignored humans the way a bird in your backyard will do.

100 generations! That sounded extremely impressive, until I remembered:

Quote:

People have lived in Australia and New Guinea since at least 60,000 years ago

Suddenly 100 generations seems woefully insufficient; shouldn't they be modeling a few thousand generations? Or is the risky period just at the beginning?

In any case, the consideration of thousands of generations just illustrates how mind-boggling long these time spans are. Compared to the way people lived for the same way for so long, our modern world is just a blink of an eye.

Quote:

According to the model, if a new group of about 130 people arrived every 70 to 90 years

Can you imagine a new wave of settlers being the big event, not even every lifetime, but every few lifetimes? Your grandparents telling stories about that time, when they were young, when new people showed up?

There are some serious ocean crossings involved in this migration. While not extreme distance they are extremely treacherous due to depth and currents. This is not something you could expect to cross with a raft. Boatbuilding nearly certainly would have been a required skill.

Why assume people were stupid then? If your people lived on a rather small island then THE tech of the day is "Boating".

Thanks for that. I think people greatly underestimate the capabilities of the people at that time. Thor Heyerdahl had access to a huge trove of information (like the fact that there actually IS land at the other end of the voyage). I am not saying it couldn't possibly have been a raft but I contend is vanishingly unlikely. I challenge any of you to build a raft big enough to colonize another land mass and convince people to join you and jump onto a raft going out to sea, remembering that in a raft there IS NO WAY TO RETURN. The Polynesians were centuries ahead of the west in terms of ocean going tech but that was still less than 2 thousand years ago. But we are talking about a culture from at least 60 thousand years ago. I've been on the ocean out where you can't see land. With engine trouble. It is amazingly scary. These folks had balls of steel even if they had mastered boats. I just don't think its very likely at all that they crossed ~50 miles of extremely treacherous water with enough people and supplies to start a colony in a one way raft.

There are some serious ocean crossings involved in this migration. While not extreme distance they are extremely treacherous due to depth and currents. This is not something you could expect to cross with a raft. Boatbuilding nearly certainly would have been a required skill.

Why assume people were stupid then? If your people lived on a rather small island then THE tech of the day is "Boating".

Thanks for that. I think people greatly underestimate the capabilities of the people at that time. Thor Heyerdahl had access to a huge trove of information (like the fact that there actually IS land at the other end of the voyage). I am not saying it couldn't possibly have been a raft but I contend is vanishingly unlikely. I challenge any of you to build a raft big enough to colonize another land mass and convince people to join you and jump onto a raft going out to sea, remembering that in a raft there IS NO WAY TO RETURN. The Polynesians were centuries ahead of the west in terms of ocean going tech but that was still less than 2 thousand years ago. But we are talking about a culture from at least 60 thousand years ago. I've been on the ocean out where you can't see land. With engine trouble. It is amazingly scary. These folks had balls of steel even if they had mastered boats. I just don't think its very likely at all that they crossed ~50 miles of extremely treacherous water with enough people and supplies to start a colony in a one way raft.

Even if the chance of success for each attempt is very small, given a very large number of tries (whether intentional or not...), eventually you'd expect to see a group make it. Whether the large number here (thousands or tens of thousands of years) compensates for each raft's poor odds, I have no idea, but it seems possible.

Even for the Polynesians I would expect there to be many, many deaths for each successful voyage into the unknown. Any successful colonization event must have been exceedingly rare in the course of countless ordinary lifetimes lived.

If you have ever been out on the open ocean 90km is a very long way. Even in a power boat. In a raft it would be nearly impossible. I stand by my statement that boatbuilding would nearly certainly be a requirement.

Have Australia's aboriginal people retained any boat making skills? I know it's a long time, but it seems weird to me that a people skilled addy seafaring would give up the seafaring (not saying it's unlikely or implausible, it just intuitively feels like the kind of thing you wouldn't abandon).

If you have a small group and not all of them know some skill, the odds of that skill vanishing are quite big.

Imagine a group where 10% know how to make a boat. They reach a new land and, for some reason, they don't need to return to the sea. After all, Australia+New Guinea are huuuge and plentiful, enough for you to lose interest on sea traveling.

Those 10% pass their knowledge to some of the new generation, say 5%, but they don't have the need to put it to practice or don't care. Some knowledge is lost during that transmission (think how hard it is to really learn a skill and how it easy to lose it without practice).

Repeat this for some generations and puf, that knowledge is gone.

I'm not saying this happened here, I don't know, but it's not hard to imagine it happening. As someone above said, the Tasmanian people didn't have that kind of technology when Europeans got there but their ancestors obviously had it. How did they lost that knowledge? Somewhere along the way, a small, isolated community, generation after generation, lost the skills it didn't need until it's too late and no one else in the group had the know-how. Kind of a tragic, slow-motion "Idiocracy" that utimately put them at the mercy of other, more advanced groups. Or extinct.

Then there are always some who just can't obey the law and set out for the frontiers.

Wouldn't be very hard to find 150 people like that every century.

Exactly. Don't assume migration is the result of a positive thought process. Think about the USA, how many groups came here out of duress, or because they were forced to? Those folks on New Guinea may have lost a war, failed to please the right chieftain, had the wrong religion or any number of unfortunate circumstances. So, it's off to the boats... "Hey, I remember a story about an island to the south..."

Then there are always some who just can't obey the law and set out for the frontiers.

Wouldn't be very hard to find 150 people like that every century.

Exactly. Don't assume migration is the result of a positive thought process. Think about the USA, how many groups came here out of duress, or because they were forced to? Those folks on New Guinea may have lost a war, failed to please the right chieftain, had the wrong religion or any number of unfortunate circumstances. So, it's off to the boats... "Hey, I remember a story about an island to the south..."

The local equivalent of the Cylons shows up and the next thing you know, you're part of a rag-tag fleet looking for the lost 13th colony...

Then there are always some who just can't obey the law and set out for the frontiers.

Wouldn't be very hard to find 150 people like that every century.

Exactly. Don't assume migration is the result of a positive thought process. Think about the USA, how many groups came here out of duress, or because they were forced to? Those folks on New Guinea may have lost a war, failed to please the right chieftain, had the wrong religion or any number of unfortunate circumstances. So, it's off to the boats... "Hey, I remember a story about an island to the south..."

It is incredibly difficult to compare relatively recent, well understood cultures with the oldest living human culture in the world.

I don't understand the reasoning it must have been an organized massive migration (or a series of organized large migrations).

If they had boats (which they must have had), I don't see why this event wasn't just a gradual expansion of a island hopping people's range, until they hit Sahul. There's nothing stopping the first few families landing on the coast from maintaining contact with the closest islands for trade, new mates, etc.